Electrically conductive polymers have been found to be useful in organic electronic devices that emit light, such as light-emitting diodes (LEDs). In all such devices an organic active emission layer is sandwiched between two electrodes which serve as the anode and the cathode. At least one of the electrodes is comprised of a material that transmits light. The active emission layer emits light through the light-transmitting electrode, typically an indium tin oxide anode, upon application of a voltage to the device. It is well known to use a layer of conductive polymer, such as a polyaniline or a poly(dioxythiophene), between the inorganic anode and the light-emitting layer. The conductive polymer layer is variously referred to as part of the anode, a hole-injection layer or a buffer layer. Such systems have been described in, for example, Jonas et al., U.S. Pat. No. 5,766,515, Yang, U.S. Pat. No. 5,723,873 and Zhang et al., U.S. Pat. No. 5,798,170.
Useful synthetic procedures for the preparation of a polyaniline (PAni) or a poly(dioxythiophene) such as poly(3,4-ethylenedioxythiophene) (PEDOT) are well known and these materials are readily available commercially.
Kinlen et al., U.S. Pat. No. 5,840,214, disclose a process for increasing the conductivity of a polyaniline comprising contacting the polyaniline with an ionic surfactant. Kinlen et al. demonstrated the process by forming an polyaniline film and subsequently contacting the polyaniline film with an ionic surfactant. They also disclose that the treatment of the polyaniline salt in xylenes prior to processing into the final form is possible where both the polyaniline salt and the anionic surfactant are soluble in an amount of at least about 1% w/w for each of the polyaniline salt and the ionic surfactant.
It is desirable to find a polymer with electrical properties that provides better performance as a buffer layer in a light-emitting device.